1. Field of the Invention
The present invention relates to a method for cutting a substrate, and more particularly, to a method for cutting a liquid crystal display panel fabricated on a large-sized mother substrate into individual liquid crystal display panel units that avoid panel degradation caused by a seal pattern.
2. Discussion of the Related Art
Image display devices have become increasingly important in the current Information Age and demands for image display devices that have high resolution images, lightness, thin profile, compact size, and low voltage power consumption are growing. Presently, a liquid crystal display (LCD), which is a major product of a flat panel display (FPD), that meets such demands is available for mass production as a substitute for cathode-ray tubes (CRTs) or television monitors.
In general, a liquid crystal display device receives data signals corresponding to picture information that are individually supplied to liquid crystal cells arranged in a matrix form in the display device. Light transmittance of the liquid crystal cells is controlled based on the data signals to display a desired picture.
The liquid crystal display apparatus generally is fabricated by forming thin film transistor array substrates on a large-sized mother substrate, forming color filter substrates on a separate mother substrate and bonding the two mother substrates to each other, thereby simultaneously fabricating multiple individual liquid crystal display panel units and thereby improving a fabrication yield. Such a fabrication requires a process for cutting the large-sized mother substrates to form individual liquid crystal display panel units.
The cutting process for the liquid crystal display panels is generally carried out by forming a prearranged cut line on the surface of the mother substrate using a wheel and applying a force on the mother substrate to form a crack (split) along the prearranged cut line, thereby cutting the mother substrate into multiple liquid crystal display panel units.
FIG. 1 is a plan view showing the structure of a liquid crystal display panel according to the related art. In FIG. 1, a unit liquid crystal display panel 10 includes an array substrate 20, a color filter substrate 30, and a liquid crystal layer (not shown) formed between the array substrate 20 and the color filter substrate 30. The array substrate 20 includes a plurality of gate lines 21 and a plurality of data lines 22 vertically and horizontally arranged thereon and defining a plurality of pixel regions. A thin film transistor (TFT) (not shown) and a pixel electrode are formed in each of the pixel regions.
The array substrate 20 has one longer side and one shorter side protruded as compared to the color filter substrate 30, where a driving circuit unit for driving the liquid crystal display panel is positioned. A gate pad region 24 is formed at the protruded shorter side of the array substrate 20 and a data pad region 23 is formed at the protruded longer side of the array substrate 20. The gate pad region 24 supplies scan signals input from a gate driving circuit unit (not shown) to the gate lines 21 and the data pad region 23 supplies image information input from a data driving circuit unit (not shown) to the data lines 22, thereby selectively driving the pixel regions to display an image in an image display region 25.
The color filter substrate 30 includes a color filter (not shown) and a common electrode (not shown), a counter electrode of the pixel electrode formed at the array substrate 20.
A cell gap is provided between the array substrate 20 and the color filter substrate 30 by a spacer (not shown). The array substrate 20 and the color filter substrate 30 are attached by a seal pattern 40 formed at an outer edge of the image display region 25. The array substrate 20 and the color filter substrate 30 are attached by an attachment key (not shown) formed on one of the array substrate 20 and the color filter substrate 30.
In general, to improve a fabrication yield, a plurality of unit liquid crystal display panels are simultaneously formed on a large scale mother substrate. The method requires a process for separating the unit liquid crystal display panels from the large size mother substrate by cutting the mother substrate.
FIG. 2 is a cross-sectional view of mother substrates according to the related art. In FIG. 2, a plurality of color filter substrates 130 are formed on a first mother substrate 100A, and a plurality of array substrates 120 are formed on a second mother substrate 100B. In addition, each of the array substrates 120 has a protruding region respective to a corresponding one of the color filter substrates 130, such that a gate pad region and a data pad region are formed in the protruding region. Thus, a first dummy region 150A is formed on the first mother substrate 100A between the color filter substrates 130 corresponding to the protruding regions of the array substrates 120.
Each unit liquid crystal display panel is arranged to utilize the first and second mother substrates 100A and 100B to the maximum, and in general unit liquid crystal display panels are formed to be separated by a second dummy region 150B. Third dummy regions 150C are formed at edges of the first and second mother substrates 100A and 100B to provide a process margin.
After the second mother substrate 100B defining the plurality of array substrates 120 and the first mother substrate 100A defining the plurality of color filter substrates 130 are attached, they are cut to form a plurality of unit liquid crystal display panels through scribing and breaking processes, i.e., a cutting process. In the cutting process, the first dummy region 150A, the second dummy region 150B, and the third dummy region 150C are simultaneously removed. Before the unit liquid crystal display panels are cut, a scribing process forms a prearranged cut line on the mother substrates 100A and 100B. The prearranged cut line is formed using a pen made of diamond having a higher hardness than glass. Then, the breaking process includes applying a mechanical force along the prearranged cut line to cut the mother substrates 100A and 100B into the unit liquid crystal display panels.
FIG. 3 illustrates a scribing process according to the related art. As shown in FIG. 3, a cutting wheel 160 needs to cut through a seal pattern 140 between the first and second mother substrates 100A and 100B. However, the cutting process is not smoothly performed at the seal pattern 140. Because a scribe line is formed only on the first mother substrate 100A, when a breaking process is performed, vertical or horizontal cracks are undesirably generated at a portion where the seal line is overlapped with the scribing line. As a result, the substrates cannot be properly cut or the cut sectional side becomes rough. When this happens, the substrate should be discarded, thereby reducing a fabrication yield.